Reason for a barrier to give affront (5,7)

I believe the answer is:

cause offence

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'give affront' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'reason for a barrier' is the wordplay.
'reason' becomes 'cause' (I've seen this in another clue).
'for a' becomes 'of' (I can't explain this - if you can you should believe this answer much more).
'barrier' becomes 'fence' (fence is a kind of barrier).
'cause'+'of'+'fence'='CAUSE OFFENCE'

'to' acts as a link.

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I've seen this clue in The Globe and Mail.

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